Electrolytic capacitors typically have a larger capacitance per unit volume than certain other types of capacitors, making them valuable in relatively high-current and low-frequency electrical circuits. One type of capacitor that has been developed is a “wet” electrolytic capacitor that includes a sintered tantalum powder anode. These tantalum “slugs” have very large internal surface area. These tantalum slugs first undergo an electrochemical oxidation that forms an oxide layer coating acting as dielectric over the entire external and internal surfaces of the tantalum body. The anodized tantalum slugs are then sealed in cans containing a highly conductive and corrosive liquid electrolyte solution, having high surface area with conductive linings allowing the flow of the current to the liquid electrolyte solution.
The electrolyte solutions used in wet tantalum electrolytic capacitors have traditionally consisted of one of two basic formulations. The first formulation consists of an aqueous solution of lithium chloride. The second electrolyte formulation traditionally used in wet tantalum capacitors consists of an aqueous solution of 35-40% sulfuric acid. Despite being corrosive, such a sulfuric acid electrolyte possesses a low resistivity, wide temperature capability, and relatively high maximum operating voltage, which have made it the choice for the vast majority of conventional wet tantalum capacitors. Nevertheless, efforts have been made to develop other electrolytes for wet capacitors. U.S. Pat. No. 6,219,222 to Shah, et al., for instance, describes an electrolyte that employs a solvent system that includes water and ethylene glycol, as well as an ammonium salt. Shah, et al. indicates that the electrolyte has a high conductivity and breakdown voltage, which lowers the equivalent series resistance. Unfortunately, problems remain in that such capacitors still have difficulty reaching high voltage values.
As such, a need currently exists for an improved wet electrolytic capacitor that is capable of achieving a high voltage.